1. Field of the Invention
The present invention relates to a swash-plate compressor which is especially incorporated in an airconditioning system used in a vehicle such as an automobile, and more particularly to such a variable capacity swash-plate compressor driven by a prime mover of the vehicle through the intermediary of an electromagnetic clutch.
2. Description of the Related Art
For example, U.S. Pat. No. 3,861,829 and Japanese Unexamined Patent Publication (Kokai) No. 1(1989)-142277 disclose representative types of variable capacity swash-plate compressors, which may be incorporated in an air-conditioning system used in a vehicle such as an automobile. These compressors comprise a cylinder block, a front housing combined with a front side of the cylinder block to define a crank chamber therebetween, a valve plate assembly attached to a rear side of the cylinder block, and a rear housing combined with the a valve plate assembly to define a suction chamber and a discharge chamber therebetween. The cylinder block has a plurality of cylinder bores formed radially and circumferentially therein and spaced from each other at regular intervals, and each of the cylinder bores slidably receives a piston. The valve plate assembly is provided with sets of suction reed valves and discharge reed valves, and each set of suction and discharge reed valves is disposed to be encompassed within an end opening area of the corresponding cylinder bore which can be communicated with the respective suction and discharge chambers through the set of suction and discharge reed valves. The suction chamber and the discharge chamber are in communication with an evaporator and a condenser of the air-conditioning system, respectively, so that a fluid or refrigerant is supplied from the evaporator to the suction chamber and a compressed refrigerant is delivered from the discharge chamber to the condenser.
The compressor also comprises a drive shaft extended through the crank chamber and rotationally driven by the prime mover of the vehicle through the intermediary of an electromagnetic clutch provided on the front housing, and a conversion mechanism provided on the shaft for converting a rotational movement of the shaft into a reciprocation of each piston in the corresponding cylinder bore such that a suction stroke and a compression stroke are alternately executed therein. During the suction stroke, the refrigerant is introduced from the suction chamber into each of the cylinder bores through the corresponding suction reed valve, and, during the compression stroke, the refrigerant is compressed and discharged from each of the cylinder bores into the discharge chamber through the corresponding discharge reed valve.
The conversion mechanism includes a drive member mounted on the shaft so as to be rotated together therewith, and an annular cam plate member pivotably connected to the drive member, with the shaft extending through a central opening of the annular cam plate member which is supported by the shaft so as to be movable in an axial direction of the shaft and swingable about a lateral axis perpendicularly intersecting with the axis of the shaft. The conversion mechanism also includes a swash-plate member slidably mounted on the cam plate member such that the swash-plate member cannot be rotated together with the cam plate member, and thus during the rotation of the cam plate member, the swash-plate member is only swung about the above-mentioned lateral axis. The conversion mechanism further includes a plurality of connecting rods to establish an operational connection between the swash-plate member and the pistons so as to cause the reciprocation of each piston in the corresponding cylinder bore. Namely, the rotational movement of the shaft is converted into the reciprocation of the pistons through the drive member, can plate member, swash-plate member, and connecting rods.
A length of the stroke executed by each piston depends upon an angle of inclination which a plane of the cam plate member defines with the axis of the shaft, and the angle of inclination is governed by a pressure in the crank chamber which is in communication with the suction chamber and/or the discharge chamber under control. Thus, the displacement or capacity of the compressor varies by a change of the pressure in the crank chamber. In general, as the pressure in the crank chamber becomes larger, the angle of inclination of the cam plate member is varied to shorten the stroke length of the piston so that the capacity of the compressor is reduced. Namely, as the pressure in the crank chamber becomes larger, the angle of inclination of the cam plate member gradually approaches to zero. Note, when the angle of inclination of the cam plate member is zero, the plane thereof defines 90 degrees with the axis of the shaft. Reversely, as the pressure in the crank chamber becomes smaller, the angle of inclination of the cam plate member is varied to lengthen the stroke length of the piston so that the capacity of the compressor is increased. Namely, as the pressure in the crank chamber becomes smaller, the cam plate member is more greatly inclined with respect to the axis of the shaft.
The compressor is frequently stopped while it is run at large or full capacity, i.e., the cam plate member is greatly or maximumly inclined with the axis of the shaft. This great or maximum inclination of the cam plate member is kept until a running of the compressor is again started. Accordingly, in the beginning of the running of the compressor, the compressor is subjected to an initial large load because the piston must be suddenly moved through a large or maximum stroke. Of course, when the compressor overcomes the sudden initial large load, not only the movable parts of the compressor inclusive of the electromagnetic clutch are susceptible to damage, but also a driver of the automobile may feel an uncomfortable movement of the vehicle.
Japanese Unexamined Utility Model Publication (JUUMP) (Kokai) No. 64(1989)-15776 discloses a variable capacity swash-plate compressor as mentioned above, which is constituted such that the cam plate member is moved so that the angle of inclination thereof approaches zero, whenever the compressor is stopped. In particular, the compressor is provided with a control valve incorporated therein for controlling the communication between the crank chamber and the suction and discharge chambers, and this control valve is operated in two modes. In one mode of operation, during the running of the compressor, the control valve is used to regulate the angle of inclination of the cam plate member in accordance with a variation of a cooling load to be borne by the air-conditioning system. In the other mode of operation, when the compressor is stopped, the control valve is used to communicate the crank chamber with the discharge chamber over a given time of period, while cutting the communication between the crank chamber and the suction chamber. Accordingly, whenever the compressor is stopped, the cam plate member is moved so that the angle of inclination thereof approaches to zero. Thus, when the compressor is again run, it is not subjected to a large load in the beginning of the running thereof.
Nevertheless, the compressor as disclosed in JUUMP No. 64(1989)-15776 is very expensive because it must be provided with an actuator such as a solenoid for actuating the control valve, and an electronic control circuit for controlling the actuator.